It is common practice to use a flat spade-type drill bit when boring holes in a relatively soft material, such as wood or plastic. This type of drill has a number of advantages (when compared to helical-type drill bits) among which advantages are the fact that it is inexpensive to manufacture and is easier to store. The commonly-used drill of this type uses a pointed lead point having flat sides whose cross-section (in a plane perpendicular to the axis of rotation of the drill) is a rectangle. Since the lead point proceeds the main cutting edges during most of the drilling operation (until the lead point emerges on the other side of the workpiece), this type of point continues to absorb a large amount of power during the entire drilling operation. Attempt was made to overcome these deficiencies by Robinson who showed and described an improved drill in his U.S. Pat. No. 2,782,824 which issued on Feb. 26, 1957. He sought to improve the operation of the drill by forming a V-shaped groove adjacent the leading edge of each side of the lead point. This did not, however, entirely solve the problem; tests proved that a considerable amount of the axial force absorbed by such a drill at a given rate of advance was still absorbed by the cutting action in the lead point. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a drill bit in which the lead point cuts with a minimum of effort.
Another object of this invention is the provision of a drill bit of the spade-type in which most of the force required for cutting is absorbed in the main cutting blades.
A further object of the present invention is the provision of a drill bit having a lead point whose cutting edge has a positive rake angle.
It is another object of the instant invention to provide a drill bit of the spade-type which is inexpensive to manufacture, which is simple to use, and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.